As those skilled in the art are aware, V.sub.T is related to the voltage at which an insulated gate semiconductor device turns on and varies in accordance with the carrier concentration of the channel region. For example, the gate-source voltage (V.sub.GS) of an n-channel insulated gate semiconductor device must exceed V.sub.T to form a channel in the insulated gate semiconductor device. Since the voltage at the gate is typically the input voltage of the insulated gate semiconductor device, the input voltage relative to the source voltage must exceed V.sub.T for a conducting channel to be formed. In other words, a significant drain current (I.sub.D) will not flow through a channel region of the insulated gate semiconductor device unless VGS is greater than V.sub.T. In addition, V.sub.T is important in determining the saturation current of art insulated gate semiconductor device, which in turn helps to determine the power bandwidth of the device.
Although precise control of V.sub.T is highly desirable in all insulated gate semiconductor device applications, it is particularly important in low voltage applications. In insulated gate semiconductor devices using standard power supply levels, the difference between the upper power supply rail (5 volts) and the lower power supply rail (0 volts) is sufficiently large, i.e., approximately 5 volts, that fluctuations in V.sub.T have a negligible effect on the device performance. However, in low voltage applications when the difference between the power supply rails is less than 1.5 volts, V.sub.T represents a substantial portion of the total power supply voltage. Consequently, fluctuations in V.sub.T results in large fluctuations of the current drive capability of the insulated gate semiconductor device.
Accordingly, it would be advantageous to have an insulated gate semiconductor device and method of manufacturing the insulated gate semiconductor device wherein the threshold voltage is suitably controlled for low voltage insulated gate semiconductor device applications.